The presence of significant quantities of H.sub.2 S in various "sour" industrial gaseous streams poses a persistent problem. Although various procedures have been developed to remove and recover this contaminant, most such processes are deficient, for a variety of reasons.
In one cyclic method currently attracting attention, the sour gas is contacted with an aqueous polyvalent metal chelate or complex reactant solution to produce solid sulfur which is recovered either prior to or subsequent to regeneration of the reactant. Preferred reactants are iron (III) complexes in which the iron (III) forms complexes with specified organic acids and derivatives thereof.
While sour gaseous streams that contain relatively low concentrations of H.sub.2 S may be treated successfully in a variety of ways if deep removal, e.g., greater than 95 percent removal of H.sub.2 S, is not required, removal of this level, or greater, demands efficiencies of operation if excessive costs of operation and materials are not to be incurred.
One scheme for carrying out the gas treatment utilizes a two-stage contacting procedure in which a venturi-shaped contacting zone is utilized as an initial or primary contacting stage to remove the bulk of the H.sub.2 S, and a follow-up or "clean-up" stage, such as a packed column or sparged tower, is provided for removing the remainder of the H.sub.2 S in the gaseous stream. These configurations have a number of drawbacks, such as susceptibility to plugging, high gas pressure drop, and high cost. It has been determined that the H.sub.2 S removal rate by iron chelate or complex systems is not limited by the reaction rate of the iron with the H.sub.2 S, but by the rate of absorption of the H.sub.2 S into the reactant solution. Accordingly, a process which provided an efficient contacting technique to insure good absorption rates of the H.sub.2 S into the contacting solution, while avoiding or minimizing plugging and high pressure drop might have great utility. U.S. Pat. No. 4,664,902, and U.S. Pat. No. 4,758,416, describe a multizone contact procedure in which a specified contact zone comprises a plurality of serial flow contact sections. In one embodiment, a first contact section of the specified contact zone comprises a plurality of discrete channels which provide a diverted flow path for the gas-solution mixture in process, the channelled section being followed by a redistribution section which is adapted to allow radial mixing and redistribution of solution in the gas, while inhibiting plugging. The invention is an improvement on this technique.